1. Field of the Invention
The invention relates to a forward feed gear mechanism for a cold pilger rolling mill having at least one forward feed carriage or slide, whose feed movement can be derived from at least one forward feed spindle which is driven in continuous rotation. It also being possible to superimpose an oscillating axial movement on the rotational movement of the forward feed spindle.
2. Description of the Prior Art
In cold pilger rolling of pipes, the pipe to be rolled is incrementally rotated and advanced synchronously with the movement of the roll stand. Between these movements, the pipe is generally held securely and does not move. Mechanical gear units which are driven by the roll stand drive are conventionally used to produce the rotating and forward feed movement. Cold pilger rolling mills are also known in which the mechanical gear units are replaced by electric or hydraulic servodrives to produce the stepwise rotational and forward feed movements. These servodrives were moved according to defined settings as a function of the roll stand drive.
A forward feed gear mechanism of the type described above is known e.g. from DE-OS 21 16 604. In this prior art, the rotational movement of the forward feed spindle for the two forward feed slides is derived from the drive of the roll stand. A costly spur gear unit is used for this purpose. A translatory axial movement is superimposed on the continuous rotational movement of the forward feed spindle in that a disk cam gear mechanism causing a reciprocating movement of the forward feed spindle via a system of levers is set in motion by the same drive. When the gear mechanism is adapted in a corresponding manner, the rotational movement of the forward feed spindle and its oscillating axial movement are added or subtracted for advancing or stopping the forward feed slide.
Such mechanical forward feed gear mechanisms are costly and prone to wear and the possibilities for adaptation are limited. Thus, in the past, forward feed gear mechanisms employing separately adjustable electric or hydraulic servodrives were frequently used.
Particularly in electric servodrives for generating forward feed movement, definite restrictions had to be submitted to with respect to the attainable forward feed values. The electric forward feed drives which were used moved the output-drive or power take-off members directly, i.e. the speed at the power take-off was always directly proportional to the speed of the drive motor. Thus, the entire output for generating movement had to be applied by the servodrives so that very narrow limits on forward feed had to be accepted.
Since the advancing or forward feed movement is not reversible, but always progresses in the same direction, the maximum speed range of the servodrives could never be fully utilized. However, the servodrives had to absorb the full load moment. The proportion of motor torque available for acceleration was therefore unnecessarily small so that achievable forward feed values were reduced by external loads (back-rolling forces) conditioned by technical factors relating to the apparatus. Since the spindles engaging with the forward feed slide are rotated in a jerky manner in forward feed servodrives, this rotation requires large acceleration moments which negatively influence the achievable forward feed values.
The gear unit stages between the servomotor and spindle must be designed with a view toward a best possible acceleration. In general, this results in large transmission ratios, i.e. high motor speeds with low spindle speeds. The gear unit stages which are selected in this way automatically condition a lengthy returning movement of the forward feed slide to its initial position even when the servomotor reverses at maximum speed. This represents a significant loss of production time for the operator.